In the conventional art, a radio base station apparatus having a base station modulation/demodulation unit combined with a transmission/reception amplifier has become mainstream, and such a radio base station apparatus is centered in plural sectors thereby to establish a service area. The radio base station apparatus illustrated in FIG. 8(a) is located at the center of the service area, and the service area centering on the radio base station apparatus is divided into the plural sectors as illustrated in FIG. 8(b) (six sectors are shown in the figure). As illustrated in FIG. 8(c), in each sector, plural-carrier signals are multiplexed (four carriers are shown in the figure). The radio base station apparatus illustrated in FIG. 8 has a capacity of twenty-four cells configured of six sectors and four carriers, and a mobile terminal in communication within the service area is managed with use of a management unit identified by a sector number and a carrier number. Inter-sector soft handover (softer handover) is performed on a mobile terminal that moves from one sector to another within the service area.
Recently, for the purposes of use in an area such as underground where radio waves do not propagate well, economical designing of a service area in a rural area and the like, a device (Optical Feeder Transmitter and Receiver: OF-TRX) equipped with a radio transceiver and a transmission/reception amplifier is deployed apart several dozen kilometers or more from a base station modulation/demodulation unit (MDE) via cable connection of an optical fiber or the like, thereby to establish the service area. FIG. 9(a) illustrates a feeder configuration of the radio base station apparatus and FIG. 9(b) is a conceptual view of the service area of feeder configuration. Only the OF-TRXs are deployed thereby to be able to establish the service area flexibly.
However, the conventional radio base station apparatus has a problem of a low degree of freedom in designing of a service area. This is because the area needs to be designed based on the fixed numbers of carriers and sectors in the design process.
In the feeder configuration, the area can be established flexibly by selecting the installed place of the optical feeder. However, as there is an upper limit to the number of sectors fixed in the design process, the area cannot be expanded with one radio base station apparatus so as to cover more sectors than the upper limit thereof. Further, as there is also an upper limit to the number of carriers per sector, it is difficult to multiplex more carriers than the upper limit thereof.
One object of the present invention is to provide a radio base station apparatus that is capable of expanding a service area flexibly, improving the degree of freedom in designing the area significantly and reducing equipment investment.